The present invention relates to apparatus for the compaction of molding sand in mold production using pressurized gas and composed of a mold flask whose floor is formed by a pattern plate with a pattern and which has a filling frame placed on top of it. Over the filling frame or over the sand placed in the flask there is a chamber, that is suddenly pressurized in a matter of milliseconds so that the molding sand is compacted while at the same time there is a drop in the gas pressure.